High frequency waveguide load comprising a dielectric window in contact with lossy coolant fluid



Dec. 26, 1967 F. O. JOHNSON FIG. 2

COOLAN-T OUT 3,360,750 HIGH FREQUENCY WAVEGUIDE LOAD COMPRISING A DIELECTRIC WINDOW IN CONTACT WITH LOSSY COOLANT FLUID Filed July 23, 1965 COOLANT COOLANT 0m w 14.3% 4 2 BANDWIDIw FREQUENCY (GC) INVENTOR TTORNEY United States Patent 3,360,750 HIGH FREQUENCY WAVEGUIDE LOAD COM- PRISING A DIELECTRIC WINDOW IN CON- TACT WITH LOSSY COOLANT FLUID Floyd 0. Johnson, Mountain View, Calif., assignor to Varian Associates, Palo Alto, Calif a corporation of California Filed July 23, 1965, Ser. No. 474,414 23 Claims. (Cl. 333-22) This invention relates in general to a novel, high power, high frequency (particularly microwave spectrum), broadband waveguide waterload and more particularly to such a waterload incorporating an inductive iris in conjunction with a dielectric slab electromagnetic wave permeable fluid impervious block window disposed transverse to the direction of electromagnetic wave propagation in a hollow waveguide. In preferred embodiments the window slab is reentrantly disposed within a lossy fluid coolant flow channel wherein the R.F. energy is dissipated and the window is na /4 thick where n is an odd integer, although preferably 1, as determnied at the center frequency of the passband of the waterload.

Improved flow channel coupling and flow channel geometrical configurations as well as means for preventing electromagnetic leakage radiation are taught in co-pending US. patent application Ser. No. 474,303 filed July 23, 1965, by R. B. Nelson now US. Patent No. 3,289,109 issued Nov. 29, 1966, which is assigned to the same assignee as the present invention.

The need for high frequency, broadband, high power electromagnetic wave energy dissipation waterolads, as dummy loads for testing high power generators such as super and high power klystrons, rnagnetrons, etc., as well as for measuring the power output of such generators through conventional calorimeter techniques is well established. Many physically elongated coaxial type waterloads are available on the market at present, however, a lack of an extremely high power waveguide waterload, which is compact and broadbanded, has heretofore not been at tained and the present invention fills such a need. The present invention teaches how an extremely small, mechanical-ly and geometrically simple, and thus cheap, waterload may be made.

In essence, the present invention provides various configurations of hollow waveguide waterloads utilizing a quarter wavelength block window in conjunction with susceptance impedance matching and broadbanding means, preferably an inductive in's, for transferring electromagnetic wave energy of high powers such as multimegawatt peak and multi-kilowatt average between, for example, a high frequency generator and the fluid coolant dissipation flow channel portion of the waterload without substantial reflection over a broad band of frequencies. An aspect of the present invention involves the elimination of problems with regard to adequately cooling the waveguide-to-window joints by positioning the quarter Wavelength window section in a re-entrant manner within a fluid coolant dissipation flow channel in a manner such that lossy coolant fluid flows in a preferably symmetrical manner about the window portion of the waterload, as will be explained in more detail hereinafter.

Therefore, an object of the present invention is to provide a novel high power, broadband, waveguide waterload for dissipating high frequency electromagnetic en- "ice Another feature of the present invention is the provision of a high power hollow waveguide waterload incorporating a hollow waveguide including a broadbanded dielectric block window disposed therein and coupled to a fluid coolant dissipation flow channel.

Another feature of the present invention is the provision of a waveguide waterload for dissipating electromagnetic wave energy incorporating a dielectric block window disposed within a waveguide at a downstream portion thereof, wherein the waveguide and window protrude in a re-entrant manner into a lossy fluid coolant flow channel such that the re-entrant portion has an electrical length of approximately nk 2, where n is any positive integer although preferably 2, as measured in said flow channel with said lossy fluid therein at f Another feature of the present invention is the provision of a high frequency waveguide waterload for dissipating electromagnetic wave energy including a dielectric block window having an electrical length of substantially na /4 as determined at the center frequency f of the passband of the waterload where n is any positive odd integer, said dielectric block window being disposed within a waveguide which is coupled to a lossy fluid coolant flow channel, and including susceptance means in said waveguide for broadbanding, said susceptance means having a net spacing S from the window which corresponds to S: (.4A +rr)\ 2) -.l)\ where n=l, O, 1, 2, 3, 4, etc.

for inductive susceptance means and where n==l, 0, 1, 2, 3, 4, etc., for capacitive susceptance means and wherein in either the inductive or capacitive case the net normalized susceptance value falls within the following limits: 3/ Y =.1 to .7, where B is net susceptance means value in mhos and Y is the reciprocal of the waveguide characteristic impedance in mhos, as determined at f Another feature of the present invention is the provision of a broadband high power waveguide waterload incorporating an E-plane T-junction relationship between the input power flow waveguide and the fluid coolant dissipation flow channel.

Another feature of the present invention is the provision of a high power broadband waveguide waterload incorporating an H-plane T-junction relationship between the input power flow waveguide and the fluid coolant dissipation flow channel.

These and other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic representation of a novel high power waveguide waterload incorporating the teachings of the present invention,

FIG. 2 is a cross-sectional view of a high power waveguide waterload incorporating the teachings of the present invention,

FIG. 3 is a sectional view of the waterload depicted in FIG. 2 taken along line 33 in the direction of the arrows,

FIG. 4 is a cross-sectional view of a novel high power waveguide waterload incorporating an H-plane T-junction relationship,

FIG. 5 is a cross-sectional view of the waterload depicted in FIG. 4 taken along the line 5-5 in the direction of the arrows.

FIG. 6 is a cross-sectional view of a novel high power waveguide waterload incorporating an E-plane T-junction,

FIG. 7 depicts an illustrative graphical portrayal of V.S.W.R. vs. frequency for a high power waveguide waterload such as depicted in FIGS. 1, 2 and 3,

FIG. 8 is a reduced fragmentary view of the waterload depicted in schematic form in FIG. 1 incorporating capacitive susceptance means in the form of a capacitive iris, and

FIG. 9 is an illustrative graphical portrayal of V.S.W.R. vs. frequency for an X-band version of a waterload such as depicted in FIGS. 4 and 5.

Referring now to FIG. 1 there is depicted a novel high power, broadband waveguide waterload 8 in schematic representation, incorporating the teachings of the present invention. The waterload 8 includes a hollow R.F. input waveguide 9 incorporating inductive iris means 10 spaced upstream (where upstream and downstream are referenced to power flow direction of electromagnetic wave energy) from an electromagnetic wave permeable dielectric window slab 11 which, according to the teachings of the present invention, is approximately onequarter of a guide wavelength thick at the center frequency f of the passband of the waveguide waterload. The windowblock 11 is then preferably x /4 thick at f However it is to be noted that a window which has a thickness of substantially na /4 where n is any odd integer, although preferably 1, is taught herein.

Fluid coolant dissipation flow channel 12 includes an input fluid coupling port 13 disposed along the wave energy propagation axis of the waterload and a pair of output fluid coupling ports 14, 15 lying in a transverse plane through the input guide within which the dielectric window slab lies. The dielectric block window 11 of the waveguide waterload is disposed in a re-entrant manner within the fluid coolant dissipation flow channel 12 such that lossy coolant fluid emanating from the input port 13 flows preferably in a symmetrical manner about the downstream window face 16 and about the interface portion 17 between the waveguide wall and the dielectric window block in order to minimize thermal stresses on the interface portion and maximize cooling of the window in order to minimize rupture and breakdown problems due to thermal stresses in use.

The basic design then of the waveguide waterload depicted in schematic form in FIG. 1 involves a combination of a quarter wavelength dielectric block window 11 disposed within the input waveguide 9 transverse to the direction of electromagnetic energy flow along the propagation axis Z, an inductive iris 10 having a susceptible value and spacing S, relative to the window such as to provide a broadband impedance transformation between the input portion of the waterload and the dissipation flow channel with a minimal amount of reflected energy from the window. Suitable lossy coolant fluids for utilization in the dissipation fluid coolant flow chamber 12 are tap water and any other commercially available lossy coolant fluids.

The nature of and value of the susceptance as well as its spacing S from the upstream window face of the dielectric block is determined with the lossy coolant fluid in the flow channel using a conventional slotted line for V.S.W.R. measurements and a Smith chart. When a quarter wavelength block window is utilized as taught herein, it can be shown that at f a zero reflection coeflicient can be theoretically obtained when s =1=dielectric constant of air e =dielectric constant of window material e =dl6lCCtflC constant of lossy coolant fluid assuming no wave-reflection from the lossy medium back through the window. However in practice it is diflicult to obtain lossy coolant fluids and window materials having the proper dielectric constants to provide an equality.

Hence the additional susceptance is required for this reason alone. Furthermore, the MM window waterload can be broadbanded by the utilization of additional susceptance disregarding the aforementioned problems in obtaining an equality between e e 6 Therefore in order to cancel any residual reflection from the window and broadband the window, susceptance is added upstream from the window such that the wave reflection from the susceptance cancels the residual wave reflection from the window.

For example, if we want to use an inductive iris for our susceptance, in order to minimally affect the power handling capabilities of the waterload, we simply, using a slotted line for V.S.W.R. measurements in conjunction with a Smith chart, in a conventional manner, locate a point down the input guide from the upstream window face, distance S, where at f the admittance is capacitive. Then we add susceptance, in the form of an inductive iris, to broadband the waterload.

Conversely, if we Want to use a capacitive iris for our su-sceptance in order to broadband the waterload by canceling residual reflection from the window, we reverse the procedure by locating a point down the guide, upstream from the window face, where the admittance is inductive at f and add an appropriate amount of susceptance, in the form of a capacitive iris, to broadband the waterload. Obviously, multiple irises can be used as well and the aforementioned broadbanding mechanism can be generically defined as the introduction of susceptance upstream from the block window such that the wave reflection from the susceptance substantially cancels the residual wave reflection from the window over a band of frequencies centered about f Naturally f is selected by cutting the window to be in /4 thick, as stated previously, at the desired f Waterloads such as depicted herein have been made with 1.10:1 V.S.W.R. over 12% bandwidths with alumina (A1 0 window materials having a dielectric constant of around 9 and lossy fluid, like tap water with a dielectric constant of around 60 at 20 C.

In order to minimize any possible problems with regard to electromagnetic wave energy being reflected back through the dielectric window 11 from the dissipation flow channel 12, in order to maintain a reflection coeflicient with respect to the iris and window combination of preferably zero at the center of the passband of the waveguide waterload, the dissipation flow channel is made sufficiently large such that any electromagnetic energy reflected from its rear wall 19 is minimal.

In order to provide an approximate electrical short at the ceramic-to-water interface transverse plane of window face 16, for electromagnetic energy within the flow channel 12, the preferred degree of re-entrancy of the window within the flow channel 12 is such that it has a re-entrant electrical length of approximately nm 2, where n is any positive integer, as indicated in FIG. 1. Preferably n will be 2 to permit complete cooling of the window-toceramic interface for thermal considerations as discussed above and also to enhance the physical joining of the flow chamber to the waveguide by removing the juncture between the flow channel and waveguide from the area of the window-to-waveguide interface 17 such that complex differential thermal expansion problems between the window, waveguide and flow channel are obviated.

Returning to the problem of broadbanding the waveguide waterload of the present invention as discussed above, it has been determined that susceptance means of an inductive or capacitive nature taking the form of preferably an inductive iris for power considerations can be utilized to considerably broadband the waterload of the present invention while simultaneously reducing the V.S.W.R. over the passband of the waterload to acceptable levels such as below e.g., 1.1 by canceling any residual reflections from the window. The susceptance means used can be inductive o-r capacitive and can be of plural or singular. Furthermore, impedance discontinuities of an -E-plane or H-plane nature can be used also in such cases where an impedance transformation between the waterload and the source might be encountered, such as in cases where the waterload is used as a mode suppressor or circuit sever for traveling wave tubes or other high frequency electron discharge devices. In any case it has been determined that where either plural axially spaced susceptances of an inductive nature are used or where a single susceptance of an inductive nature is used, in cases either of an H-plane discontinuity type or of an inductive iris type, that the net spacing S should be where n is 1, 0, 1, 2, 3, 4, 5, etc., as determined at f The above relationship includes inductive irises painted on the window face for n -l case. In the case of a single inductive iris or H-plane discontinuity the net spacing S would be as shown in FIGS. 1, 2, etc. In the case of plural inductive discontinuities the net spacing S would be the resultant phase of the vector sum of the individual susceptances expressed in terms of as indicated above.

The particular susceptance value required to provide acceptable V.S.W.R. over the passband of the coupler to obtain bandwidths e.g., of better than 16% at V.S.W.R. of better than 1.2 have been determined to lie within the following ranges: B/Y :.1 to .7 as determined at 1, where B is net susceptance means value of mhos, where Y is the reciprocal of the waveguide characteristic impedance in mhos, and B/Y is therefore the normalized net susceptance.

In the case of a single H-plane discontinuity or inductive iris, the net B/Y, is simply the susceptance value of the iris or impedance discontinuity. In the case of a combination of axially spaced susceptances, the net B/Y is simply the resultant magnitude of the vector sum of the individual susceptances.

It'has also been determined that where either plural axially spaced susceptances of a capacitive nature are used or where a single susceptance of a capacitive nature is used, in cases of either an E-plane discontinuity type or of a capacitive iris type, that the net spacing S should be (.65h +n /2) .10 where n=1, 0, 1, 2, 3, 4, 5, etc., as determined at f In the case of a single capacitive iris or E-plane discontinuity, S would be as shown in fragmentary FIG. 8 which is simply the embodiment. of FIG. 1 having a capacitive iris 45 rather than an inductive iris for broad- V banding. In the case of plural capacitive susceptances, the

net spacing S would be the resultant phase of the vector sum of the individual susceptances expressed in terms of A as indicated above.

The particular susceptance value required to provide acceptable V.S.W.R. over the passband of the coupler to obtain bandwidth e.g., of better than 16% at V.S.W.R. of better than 1.2 have been determined to be identical to the inductance case discussed above, namely, B/Y =.1 to .7 as determined at f where B is againthe net susceptance means value in mhos, Y =reciprocal of the waveguide 9 characteristic impedance in mhos, and B/Y is therefore the normalized net susceptance.

Where a single E-plane discontinuity or capacitive iris is used, the net B/Y is simply the susceptance value of the iris of the impedance discontinuity. In the case of a combination of axially spaced susceptances, the net B/Y is simply the resultant magnitude of the vector sum of the individual susceptances.

In the above cases the bandwidth is determined in a conventional manner as and V.S.W.R. is 1.2 or less.

Where f and f are determined at a 1.2 V.S.W.R. it is significant that using the aforementioned broadbanding techniques bandwidths of better than 16% have been obtained with S- and X-band waterloads handling multimegawatt peak and multi-kilowatt average powers and better than 14% at 1.1 V.S.W.R.

In both the S-band and X-band waterload designs, excellent results with respect to V.S.W.R. were achieved with S=.4 at f using an inductive iris with B/Y =about .2 in the S-band case and B/Y =between .4 and .45. It is feasible to employ values of B/Y ranging up to 50.

Turning now to FIGS. 2 and 3 there is shown in detail a high power broadband waveguide waterload built according to the schematic representation of FIG. 1 which was capable of handling better than 10 megawatts peak power and 14 kilowatts average power at S-band. Briefly, the waveguide waterload depicted in FIGS. 2 and 3 includes a standard electrolytic copper or the like input waveguide 20 incorporating a copper or the like mount ing flange 21 at the input portion to facilitate coupling of the waterload to the power source in a conventional manner. The waveguide 20 incorporates an inductive iris 22 spaced upstream with reference to the power flow of the electromagnetic energy denoted by the arrow along the waterload axis Z. At the downstream end of guide 20 a copper extension flange member 23' is brazed or the like thereto and terminated :by an electromagnetic wave permeable wind-ow slab or block 23, preferably of alumina (A1 0 single crystal sapphire, bery llia, etc. The window is brazed to the flange in a conventional manner to provide a vacuum seal. The wave permeable dielectric window block 23 is designed to be approximately nk 4 thick as determined at the center frequency f of the passband of the waveguide waterload as discussed previously, where n is any odd integer.

The fluid coolant dissipation flow channel 24 of copper or the like of the waveguide waterload has an input fluid coupling port 25 disposed at the downstream end of the waterload in a symmetrical manner about the Z-axis of the waterload. A pair of output fluid coupling ports 26, 27 which, as shown, can be copper tubulations, are brazed or the like to the coolant channel walls as shown. The dielectric wave permeable block window 23 is preferably disposed so as to lie in a transverse plane extending through the common axis of the output ports 26, 27 denoted :by Y in order to provide a re-entrant window with respect to the dissipation channel thereby assuring good symmetrical flow conditions of the lossy coolant fluid about the interface junction 28 between dielectric window 23 and the support flange 23'.

An S-band waveguide waterload constructed according to the configuration depicted in FIGS. 2 and 3 utilizing standard WR340 S-band rectangular guide for input waveguide 20 and an alumina block window 23 which was designed to be one-quarter a thick at a center frequency f of 2.8 gigacycles and utilizing tap water for the coolant flow having a flow rate of 3 /2 gallons per minute easily dissipated 1O megawatts peak power at a PRR of 600 c.p.s. with various pulse widths up to 10 asec. producing better than 14 kilowatts average power without destruction of the window or excessive thermal stresses of the window to support flange interface. V.S.W.R. measurements were made for such an S-band waterload and examination of FIG. 7 will show that V.S.W.R. of less than 1.2 was obtained in a frequency range of 2.6 to over 3 gigacycles. The susceptance value of the inductive iris 22 and the spacing S between the inductive iris and the upstream face of the dielectric wave permeable window was set so as to approximately cancel the residual reflection from the window over the entire frequency band as discussed above.

The above power measurements were made with a waterload having dissipation flow channel physical length L of 2 inches and width W of 3% inches and height H of 1 inches and an overall length L' of 8 inches which indicates the extremely high powers capable of being handled in a-very compact waterload incorporating the teachings of the present invention. Obviously the aforementioned design parameters are merely illustrative and are not to be construed as limiting in nature. In order to efliciently dissipate R.F. energy in the dissipation flow channel 24 the length L is made at least a plurality of electrical wavelengths long at the center frequency of operation as measured in the lossy coolant fluid filling the flow channel.-Assuming ordinary tap water and the aforementioned channel dimensions of L, H and W, we arriveat a chamber of 5 electrical wavelengths long at an f of 2.8 g.p.s. which is more than adequate to result in total dissipation of peak and average powers of the aforementioned magnitudes without any substantial reflection back through the window. Ordinary tap water which has a dielectric loss tangent of approximately 0.15 is adequate for the lossy coolant fluid. Naturally other suitable lossy cooolant fluids such as distilled water, wateralcohol, etc., may advantageously be utilized with the novel waveguide waterload of the present invention without departing from the scope thereof;

It is to be noted that an advantage to be derived from utilizing a fluid cooling dissipation flow channel having larger physical dimensions than the input waveguide is the facilitation of a re-entrant disposition of the window portion within the dissipation flow channel to provide the aforementioned thermal electrical and structural advantages.

Turning now to FIG. 4 there is depicted a variation of the novel high power waveguide waterload incorporating the concepts of the present invention in an H-plane T-junction configuration. In the embodiment of FIG. 4 the waveguide waterload which will be termed an H-plane waterload for convenience includes a rectangular waveguide 30 in conjunction with a fluid coolant dissipation flow channel 31 which is formed from a simple pipe having a unidirectional fluid flow axis denoted X. The waveguide 30 includes a wave permeable dielectric block window 32 vacuum brazed at the downstream end portion to the waveguide 30 to form -a fluid impervious vacuum seal therebetween. Disposed upstream from the window 32 is an inductive iris 33 spaced according to the aforementioned teachings with regard to FIG. 1 in order to obtain a broadband waterload. The H-plane waveguide waterload depicted in FIGS. 4 and 5 is characterized by having a unidirectional fluid coolant flow channel 31 disposed in the H-plane of the input waveguide 30 to form a T-junction as shown. Downstream from the window, the energy is radiated as a plane wave into the fluid.

- The wave spreads a little into the T-sections but is rapidly attenuated. The attenuated wave front is reflected from the rear wall of the chamber. This wall is far enough from the window that the doubly attenuated wave returning through the window is so weak that it does not appreciably affect the impedance match. The re-entrant arrangement permits the lossy coolant fluid to flow past the waveguide to ceramic block interface portions 34 thus enhancing the operation thereof at high powers as discussed previously.

An H-plane waterload such as shown in FIGS. 4 and 5 was constructed for X-band operation and easily handled better than 30 kw. CW at an f of 8 gc. with a power cross-section of 54 kilowatts per square inch using tap water having a flow velocity sufficient to limit AT to less than 30 C., where AT is simply the difference between the input and output fluid temperatures as determined at the input and output ports of the flow channel. It is of course good practice to minimize AT to as great a degree as feasible in order to minimize changes in the dielectric constant of the lossy coolant fluid which would otherwise adversely aifect the passband characteristics of the waterload. The above X-band load was constructed with dimension H of 3.5 inches, L of 2.5 inches and OD of 1% inches, which illustrates the extreme compactness of waterloads incorporating the teachings of the present invention.

In FIG. 9 an illustrative V.S.W.R. vs. frequency characteristic is depicted for an X-band lo-ad designed according to the aforementioned teachings. The solid curve represents the measured V.S.W.R. with broadbanding and the dotted curve represents the measured V.S.W.R. without broadbanding. A visual comparison of the two curves presents an excellent graphical illustration of the advantages derived from the teachings of the present invention.

In FIG. 6 an E-plane T-junction waveguide waterload is depicted. The E-plane waveguide waterload involves simply a space rotation of the coolant pipe 35 which forms flow channel 36 with respect to the input waveguide 37 in relation to the H-plane waterload depicted in FIGS. 4 and 5. Once again the wave permeable window 38 is vacuum sealed to the downstream portion of waveguide 37 and disposed in a re-entrant manner Within the coolant fluid flow channel 36. Preferably, inductive irises 39 are utilized to broadband the waterload. The E-plane waterload depicted in FIG. 6, for a given size pipe 35, results in a reduction in flow channel volume in the vicinity of the window as shown and the waterload designer thus is provided with greater design flexibleness.

The terminology E-plane T-junction and H-plane T-junction are per ASA definitions. In an E-plane T- junction the change in structure occurs in the plane of the electric field and in H-plane T-junction the change in structure occurs in the plane of the magnetic field. Thermal advantages to be derived in both the E-plane and H-plane cases when utilized with a re-entrantly disposed window, as shown, are good fluid flow past the window to waveguide interface portions coupled with increased fluid fiow velocity past the downstream window faces 40, 41 with a resultant enhanced power dissipation in the vicinity of the window for given flow parameters.

The high power waveguide waterload configurations of the present invention depicted in conjunction with rectangular input waveguides are advantageously applicable to circular and other types of hollow waveguides without departing from the scope of the present invention.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description and as shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A waveguide waterload for dissipating high frequency electromagnetic wave energy including a waveguide having an electromagnetic wave permeable and fluid-impervious dielectric block window disposed therein, fluid cool-ant dissipation flow channel means coupled to said waveguide in a manner such that lossy coolant fluid passing through said flow channel means will come in intimate contact with said dielectric block window, said waveguide having susceptance means incorporated therein for canceling residual reflections of electromagnetic wave energy from said dielectric window, said flow channel having separate means for introducing and extracting lossy coolant fluid the-rein and therefrom, respectively, said block window having the same height and width dimensions as the internal height and width dimensions of said waveguide.

2. The waterload defined in claim 1 wherein said dielectric block window has a thickness dimension which is substantially na /4, as determined at the center frequency, 19 of the passband of the waterload, where n is any odd integer.

3. A waveguide waterload for dissipating high frequency electromagnetic wave energy including a waveguide having an electromagnetic wave permeable and fluid-impervious dielectric block window disposed therein, fluid coolant dissipation flow channel means coupled to said waveguide in a manner such that lossy coolant fluid passing through said flow channel means will come in intimate contact with said dielectric block window, said waveguide having susceptance means incorporated therein for canceling residual reflections of electromagnetic wave energy from said dielectric window, said flow channel having separate means for introducing and extracting lossy coolant fluid therein and therefrom, respectively, said dielectric window block and the waveguide portion within which said window is disposed protruding into said fluid coolant dissipation flow channel in a re-entrant manner with the re-entrant portion thereof having an electrical length of approximately nk 2 where n is any positive integer and wherein is determined at the center frequency f of the passband of the coupler with said lossy coolant fluid therein.

4. A waveguide waterload for dissipating high frequency electromagnetic wave energy including a waveguide having an electromagnetic wave permeable and fluid-impervious dielectric block window disposed therein, fluid coolant dissipation flow channel means coupled to said waveguide in a manner such that lossy coolant fluid passing through said flow channel means will come in intimate contact with said dielectric block window, said waveguide having susceptance means incorporated therein for canceling residual reflections of electromagnetic wave energy from said dielectric window, said flow channel having separate means for introducing and extracting lossy coolant fluid therein and therefrom, respectively, said susceptance means being inductive in nature and having a net spacing S from the window which corresponds to where n=-l, 0, 1, 2, 3, 4, 5, etc., asdetermined at the center frequency f of the passband of the waterload, said inductive susceptance means having a net normalized susceptance value B/Y falling within the following limits B/ Y :.1 to .7 as determined at f where B is net susceptance means value in mhos and Y is the reciprocal of the waveguide characteristic impedance where-by said waterload is broadbanded.

5. A waveguide waterload for dissipating high frequency electromagnetic wave energy including a waveguide having an electromagnetic wave permeable and fluid-impervious dielectric block window disposed therein, fluid coolant dissipation flow channel means coupled to said waveguide in a manner such that lossy coolant fluid passing through said flow channel means will come in intimate contact with said dielectric block window, said waveguide having susceptance means incorporated therein for canceling residual reflections of electromagnetic wave energy from said dielectric window, said flow channel having separate means for introducing and extracting lossy coolant fluid therein and therefrom, respectively, said susceptance means being capacitive in nature and having a net spacing S from the window which corresponds to S=(.65 +nx /2):.l0x where n=-l, O, l, 2, 3, 4, 5, etc., as determined at the center frequency t of the passband of the waterload, said capacitive susceptance means having a net normalized susceptance value B/Y falling within the following limits B/ Y =.l to .7 as determined at f,,, where B is net susceptance means value in mhos and Y is the reciprocal of the waveguide characteristic impedance.

6. A hollow waveguide waterload for dissipating high I frequency electromagnetic wave energy including a hollow waveguide adapted and arranged to receive electromagnetic wave energy at an input (upstream) portion thereof, said hollow waveguide having an electromagnetic wave permeable and fluid impervious dielectric block window sealed therein at the output (downstream) portion thereof, an electromagnetic wave energy fluid coolant dissipation flow channel disposed about said hollow waveguide at the downstream portion thereof, said downstream end portion of said hollow waveguide being disposed in a reentrant manner within said fluid coolant dissipation flow channel, said flow channel being provided with means for introducing and extracting lossy coolant fluid into said 10 channel such that said fluid cools said window while absorbing said electromagnetic wave energy.

7. The waveguide waterload defined in claim 6 wherein said electromagnetic wave permeable dielectric block window is approximately one-quarter wavelength long as measured along the power flow axis of electromagnetic wave energy propagation therethrough at the center frequency of the passband of the waveguide waterload.

8. The waveguide waterload defined in claim 6 wherein said electromagnetic wave permeable dielectric block window is approximately one-quarter wavelength thick as measured in the direction of wave energy propagation therethrough at the center frequency of the pass-band of said waterload and wherein said hollow waveguide includes susceptive iris means disposed therein upstream from said wave permeable block window in a manner such that said waveguide waterload is broadbanded by having wave reflection from the iris substantially cancel the residual reflection from the window over a band of frequencies.

9. The waveguide waterload defined in claim 6 wherein said fluid coolant dissipation flow channel includes a fluid coolant input coupling means disposed along the axis of propagation of said electromagnetic wave energy and wherein said dissipation channel includes a pair of output fluid coolant coupling means having a common axis disposed in a transverse plane through said block window, said plane being disposed normal to the wave energy propagation axis of the input waveguide.

19. The hollow waveguide waterload defined in claim 6 wherein said fluid coolant dissipation flow channel is a unidirectional fluid flow channel having its fluid flow propagation axis disposed normal to the electromagnetic power flow propagation axis of the input waveguide.

11. The hollow waveguide waterload defined in claim 10 wherein said fluid coolant dissipation flow channel is a unidirectional fluid flow channel having its fluid flow axis disposed parallel to the H-fleld plane of the input waveguide.

12.' The hollow waveguide waterload defined in claim 10 wherein said fluid coolant dissipation flow channel is a unidirectional fluid flow channel having it fluid flow axis disposed parallel to the E-field plane of the input waveguide.

13. A waveguide waterload for dissipating high frequency electromagnetic wave energy including a hollow input waveguide having a dielectric electromagnetic wave permeable and fluid impervious block window sealed therein at the one end portion thereof, said waterload having a fluid coolant flow channel disposed about the one waveguide end portion having the dielectric wave permeable window, disposed therein, said fluid coolant flow channel having input and output means for passing lossy coolant fluid therein and thereout, respectively, said fluid coolant flow channel having greater transverse cross-sectional internal dimensions than said input waveguide and said block window having the same external dimensions as the internal dimensions of said hollow waveguide.

14. A waveguide waterload for dissipating high frequency electromagnetic wave energy in a lossy coolant fluid flowing through a fluid coolant dissipation flow channel including an input waveguide for high frequency electromagnetic wave energy, said input waveguide having an electromagnetic wave permeable and fluid impervious dielectric block window disposed therein at a downstream portion of said input waveguide, said dielectric block window having a thickness dimension as measured along the power flow propagation axis of the input waveguide which is approximately nx 4 as measured at the center frequency f of the passband of the waterload, where n is any odd integer, said input waveguide having a lumped susceptance disposed therein upstream from said dielectric block window, said input waveguide having a lossy fluid coolant flow channel coupled to the downstream portion thereof, said dielectric block window forming a fluid defining boundary for said flow channel, said flow channel having input and output fluid coupling means coupled thereto for introducing lossy coolant fluid therein, said block window having the same external dimensions as the internal dimensions of said waveguide.

15. A waveguide waterload for dissipating high frequency electromagnetic wave energy in a lossy coolant fluid flowing through a fluid coolant dissipation flow channel including an input waveguide for high frequency electromagnetic waveenergy, said input waveguide having an electromagnetic wave permeable and fluid impervious dielectric block window disposed therein at a downstream portion of said input waveguide, said dielectric block window having a thickness dimension as measured along the power flow propagation axis of the input waveguide which is approximately na /4 as measured at the center frequency f of the passband of the waterload, where n is any odd integer, said input waveguide having a lumped susceptance disposed therein upstream from said dielectric block window, said input waveguide having a lossy fluid coolant flow channel coupled to the downstream portion thereof, said dielectric block Window forming a fluid defining boundary for said flow channel, said flow channel having input and output fluid coupling means coupled thereto for introducing lossy coolant fluid therein, said fluid coolant flow channel being adapted and arranged such that lossy coolant fluid enters said flow channel-along the electromagnetic wave energy power flow propagation axis of said input waveguide and leaves said flow channel along an axis which lies in a transverse plane through said dielectric wave permeable block window.

16. A waveguide waterload for dissipating. high frequency electromagnetic wave energy in a lossy coolant fluid flowing through a fluid coolant dissipation flow channel including an input waveguide for high frequency electromagnetic wave energy, said input waveguide having an electromagnetic wave permeable and fluid impervious dielectric block window disposed therein at a downstream portion of said input waveguide, said dielectric block window having a thickness dimension as measured along the power flow propagation axis of the input waveguide which is approximately mt /4 as measured at the center frequency f of the passband of the waterload, where n is any odd integer, said input waveguide having a lumped susceptance disposed therein upstream from said dielectric block window, said input waveguide having a lossy fluid coolant flow channel coupled to the downstream portion thereof, said dielectric block window forming a fluid defining boundary for said flow channel, said flow channel having input and output fluid coupling means coupled thereto for introducing lossy coolant fluid therein, said waveguide waterload being geometrically arranged to define an E-plane T-junction between said input Waveguide and said fluid coolant flow channel.

17. A waveguide waterload for, dissipating high frequency electromagnetic wave energy including a waveguide having an electromagnetic wave permeable and fluid-impervious dielectric block window disposed therein, fluid coolant dissipation flow channel means coupled to said waveguide in a manner such that lossy coolant fluid passing through said flow channel means will come in intimate contact with said dielectric block window, said waveguide having susceptance means incorporated therein for canceling residual reflections of electromagnetic wave energy from said dielectric window, said flow channel having separate means for introducing and extracting lossy coolant fluid therein and therefrom, respectively, said susceptance meansbeing capacitive in nature and having a net spacing S from the Window which corresponds to S=(.65 +n /2) 1.10%, where n=l, 0, 1, 2, 3, 4, 5, etc., as determined at the center frequency i of the passband of the waterload, said capacitive susceptance means having a net normalized susceptance value B/Y falling within the following limits B/Y =.l to .7 as determined at f,,, where B is net susceptance means value in mhos and Y is the reciprocal of the waveguide characteristic impedance, said waveguide waterload being geometrically arranged to define an H-plane T-junction between said input waveguide and said fluid coolant flow channel.

18. A waveguide waterload for high frequency electromagnetic wave energy, said waterload including a hollow input waveguide having an electromagnetic wave permeable dielectric block window sealed therein, said dielectric block window having a thickness dimension as measured in the direction of power flow of said electromagnetic wave energy therethrough which is substantially one quarter k as determined at the center frequency of the passband of said waterload, said hollow input waveguide having inductive iris means disposed upstream thereof with respect to said wave permeable dielectric block window, said waterload including a fluid coolant flow channel disposed downstream from said electromag netic wave permeable dielectric block window, said flow channel being provided with fluid coupling means for passing lossy coolant fluid through said flow chamber in intimate contact with the downstream face of said block window, said block window having the same external dimensions as the internal dimensions of the hollow waveguide.

19. A high frequency waveguide waterload including a rectangular waveguide having a rectangular dielectric electromagnetic wave permeable and fluid impervious block window vacuum sealed therein and an iris disposed in said rectangular waveguide upstream from said block window, said dielectric block window having a thickness dimension as measured in the direction of electromagnetic wave energy power flow propagation therethrough which is substantially mt /4 where n is any odd integer as determined at the center frequency of the passband of said waterload, said rectangular waveguide being disposed with its downstream end portion having said dielectric block window vacuum sealed therein disposed in relation to a coolant fluid dissipation flow channel in a manner such that lossy coolant fluid may come in contact with the interface between said dielectric wave permeable block window and the surrounding rectangular waveguide interface portion and in intimate contact with the downstream face of said block window.

20. The waveguide waterload defined in claim 19 wherein said coolant fluid dissipation flow channel is adapted and arranged to provide unidirectional lossy coolant fluid flow therethrough along an axis which is disposed perpendicular to the electromagnetic Wave energy power flow axis of said rectangular waveguide.

21. A high frequency waveguide waterload including a rectangular waveguide having a rectangular dielectric electromagnetic wave permeable and fluid impervious block window vacuum sealed therein and an iris disposed in said rectangular waveguide upstream from said block window, said dielectric block window having a thickness dimension as measured in the direction of electromagnetic wave energy power flow propagation therethrough which is substantially na /4 where n is any odd integer as determined at the center frequency of the passband of said waterload, said rectangular waveguide being disposed with its downstream end portion having said dielectric block window vacuum sealed therein disposed in relation to a coolant fluid dissipation flow channel in a manner such that lossy coolant fluid may flow past the interface between said dielectric wave permeable block window and the surrounding rectangular waveguide interface portion and in intimate contact with the downstream face of said block window, said coolant fluid dissipation flow channel having a fluid coolant input port disposed symmetrically with respect to the power flow propagation axis of said rectangular waveguide and said fluid coolant dissipation flow channel having a pair of space rotated output fluid coolant coupling ports disposed within a pl n rough said Wave permeable dielectric quarter 13 wavelength block window, said plane being transversely oriented with respect to said power flow propagation axis.

22. A waveguide waterload as defined in claim 19 wherein said fluid coolant dissipation flow channel has an axial distance as measured between said output face (downstream face) of said wave permeable dielectric block Window along the power flow propagation axis of said rectangular waveguide to the defining Wall portion of said channel which is greater than one wavelength for electromagnetic wave energy at the center frequency of the passband of said waterload with lossy fluid coolant flowing within said flow channel.

23. A hollow waveguide waterload for dissipating high frequency electromagnetic wave energy comprising a hollow waveguide defining a central axis and having an electromagnetic wave permeable and fluid-impervious dielectric window disposed therein, said window having the same height and width dimensions as the internal height and width dimensions of said hollow waveguide, fluid coolant dissipation flow channel means coupled to said waveguide for establishing a fluid flow path transverse to the waveguide central axis, the portion of said hollow waveguide containing said dielectric window protruding into said flow channel means, said flow channel having larger internal dimensions than said hollow waveguide.

References Cited OTHER REFERENCES Introduction to Microwave MeasurementsApplication Note 46, Helwett-Packard Company, Palo Alto, Calif., 1960 (title page and page describing model 870A tuner relied upon).

HERMAN KARL SAALBACH, Primary Examiner.

R. F. HUNT, M. NUSSBAUM, Assistant Examiners. 

1. A WAVEGUIDE WATERLOAD FOR DISSIPATING HIGH FREQUENCY ELECTROMAGNETIC WAVE ENERGY INCLUDING A WAVEGUIDE HAVING AN ELECTROMAGNETIC WAVE PERMEABLE AND FLUID-IMPERVIOUS DIELECTRIC BLOCK WINDOW DISPOSED THEREIN, FLUID COOLANT DISSIPATION FLOW CHANNEL MEANS COUPLED TO SAID WAVEGUIDE IN A MANNER SUCH THAT LOSSY COOLANT FLUID PASSING THROUGH SAID FLOW CHANNEL MEANS WILL COME IN INTIMATE CONTACT WITH SAID DIELECTRIC BLOCK WINDOW, SAID WAVEGUIDE HAVING SUSCEPTANCE MEANS INCORPORATED THEREIN FOR CANCELING RESIDUAL REFLECTIONS OF ELECTROMAGNETIC WAVE ENERGY FROM SAID DIELECTRIC WINDOW, SAID FLOW CHANNEL HAVING SEPARATE MEANS FOR INTRODUCING AND EXTRACTING LOSSY COOLANT FLUID THEREIN AND THEREFROM, RESPECTIVELY, SAID BLOCK WINDOW HAVING THE SAME HEIGHT AND WIDTH DIMENSIONS AS THE INTERNAL HEIGHT AND WIDTH DIMENSIONS OF SAID WAVEGUIDE. 